function Node(value) {
	this.value = value;
	this.next = null;
	this.pre = null
}

var node1 = new Node(1);
var node2 = new Node(2);
var node3 = new Node(3);
var node4 = new Node(4);
var node5 = new Node(5);

node1.next = node2;
node2.pre = node1;
node2.next = node3;
node3.pre = node2;
node3.next = node4;
node4.pre = node3;
node4.next = node5;
node5.pre = node4;

//双向链表的优点： 无论给出哪一个节点，都能对整个链表进行遍历
//        缺点：多耗费一个引用空间， 而且构建双线链表比较复杂